Fractalkine, also known as chemokine (C-X3-C motif) ligand 1, is a protein that in humans is encoded by the CX3CL1 gene.
Fractalkine, also known as chemokine (C-X3-C motif) ligand 1, is a protein that in humans is encoded by the CX3CL1 gene.
Fractalkine is a large cytokine protein of 373 amino acids that contains multiple domains and is the only known member of the CX3C chemokine family. It is also commonly known under the names fractalkine (in humans) and neurotactin (in mice). [5] [6] The polypeptide structure of CX3CL1 differs from the typical structure of other chemokines. For example, the spacing of the characteristic N-terminal cysteines differs; there are three amino acids separating the initial pair of cysteines in CX3CL1, with none in CC chemokines and only one intervening amino acid in CXC chemokines. CX3CL1 is produced as a long protein (with 373-amino acid in humans) with an extended mucin-like stalk and a chemokine domain on top. The mucin-like stalk permits it to bind to the surface of certain cells. However a soluble (90 kD) version of this chemokine has also been observed. Soluble CX3CL1 potently chemoattracts T cells and monocytes, while the cell-bound chemokine promotes strong adhesion of leukocytes to activated endothelial cells, where it is primarily expressed. [6] CX3CL1 elicits its adhesive and migratory functions by interacting with the chemokine receptor CX3CR1. [7] Its gene is located on human chromosome 16 along with some CC chemokines known as CCL17 and CCL22. [6] [8]
Fractalkine is found commonly throughout the brain, particularly in neural cells, and its receptor is known to be present on microglial cells. It has also been found to be essential for microglial cell migration. [9] CX3CL1 is also up-regulated in the hippocampus during a brief temporal window following spatial learning, the purpose of which may be to regulate glutamate-mediated neurotransmission tone. This indicates a possible role for the chemokine in the protective plasticity process of synaptic scaling. [10]
Chemokines, or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In addition to playing a major role in the activation of host immune responses, chemokines are important for biological processes, including morphogenesis and wound healing, as well as in the pathogenesis of diseases like cancers.
Chemokine ligand 8 (CCL8), also known as monocyte chemoattractant protein 2 (MCP2), is a protein that in humans is encoded by the CCL8 gene.
Chemokine ligand 21 (CCL21) is a small cytokine belonging to the CC chemokine family. This chemokine is also known as 6Ckine, exodus-2, and secondary lymphoid-tissue chemokine (SLC). CCL21 elicits its effects by binding to a cell surface chemokine receptor known as CCR7. The main function of CCL21 is to guide CCR7 expressing leukocytes to the secondary lymphoid organs, such as lymph nodes and Peyer´s patches.
C-C motif chemokine 22 is a protein that in humans is encoded by the CCL22 gene.
CCL17 is a powerful chemokine produced in the thymus and by antigen-presenting cells like dendritic cells, macrophages, and monocytes. CCL17 plays a complex role in cancer. It attracts T-regulatory cells allowing for some cancers to evade an immune response. However, in other cancers, such as melanoma, an increase in CCL17 is linked to an improved outcome. CCL17 has also been linked to autoimmune and allergic diseases.
Chemokine ligand 19 (CCL19) is a protein that in humans is encoded by the CCL19 gene.
CX3C motif chemokine receptor 1 (CX3CR1), also known as the fractalkine receptor or G-protein coupled receptor 13 (GPR13), is a transmembrane protein of the G protein-coupled receptor 1 (GPCR1) family and the only known member of the CX3C chemokine receptor subfamily.
Chemokine ligand (XCL1) is a small cytokine belonging to the C chemokine family that is also known as lymphotactin. Chemokines are known for their function in inflammatory and immunological responses. This family C chemokines differs in structure and function from most chemokines. There are only two chemokines in this family and what separated them from other chemokines is that they only have two cysteines; one N-terminal cysteine and one cysteine downstream. These both are called Lymphotactin, alpha and beta form, and claim special characteristics only found between the two. Lymphotactins can go through a reversible conformational change which changes its binding shifts.
Chemokine ligand 2 (XCL2) is a small cytokine belonging to the XC chemokine family that is highly related to another chemokine called XCL1. It is predominantly expressed in activated T cells, but can also be found at low levels in unstimulated cells. XCL2 induces chemotaxis of cells expressing the chemokine receptor XCR1. Its gene is located on chromosome 1 in humans.
C-C chemokine receptor type 7 is a protein that in humans is encoded by the CCR7 gene. Two ligands have been identified for this receptor: the chemokines ligand 19 (CCL19/ELC) and ligand 21 (CCL21). The ligands have similar affinity for the receptor, though CCL19 has been shown to induce internalisation of CCR7 and desensitisation of the cell to CCL19/CCL21 signals. CCR7 is a transmembrane protein with 7 transmembrane domains, which is coupled with heterotrimeric G proteins, which transduce the signal downstream through various signalling cascades. The main function of the receptor is to guide immune cells to immune organs by detecting specific chemokines, which these tissues secrete.
Protease activated receptor 3 (PAR-3) also known as coagulation factor II receptor-like 2 (F2RL2) and thrombin receptor-like 2, is a protein that in humans is encoded by the F2RL2 gene.
C-C chemokine receptor type 4 is a protein that in humans is encoded by the CCR4 gene. CCR4 has also recently been designated CD194.
C-C chemokine receptor type 3 is a protein that in humans is encoded by the CCR3 gene.
C-C chemokine receptor type 11 is a protein that in humans is encoded by the CCRL1 gene.
Chemokine-binding protein 2 is a protein that in humans is encoded by the CCBP2 gene.
C-X-C chemokine receptor type 6 is a protein that in humans is encoded by the CXCR6 gene. CXCR6 has also recently been designated CD186.
Interleukin 1 receptor, type I (IL1R1) also known as CD121a, is an interleukin receptor. IL1R1 also denotes its human gene.
CD84 is a human protein encoded by the CD84 gene.
Interleukin 3 receptor, alpha (IL3RA), also known as CD123, is a human gene.
C-C motif chemokine ligand 27 is a protein that in humans is encoded by the CCL27 gene.
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